Continuous line yarder with traction and extensible sheave assemblies

ABSTRACT

A continuous or single line yarding system employs a single winch drum. The yarding system employs a boom mounted on a platform at a first location and an outhaul block at a location remote from the first. A single main yarding line engages two sets of traction sheaves rotatably mounted on the boom. The traction sheaves are driven by a prime mover through a suitable transmission mechanism. Both ends of the single line extend to the upper end of the boom to form the inhaul line and outhaul line portions of the single main line. The outhaul line is strung from the boom to the outhaul block and inwardly toward the boom where it connects to a grapple carriage intermediate the boom and the outhaul block. The grapple carriage is suspended by a sheave from the outhaul line between the boom and the outhaul block. The inhaul line extends outwardly from the boom and is also connected to the grapple carriage. Two sets of sheaves which are translatable away from and toward each other are mounted on the boom intermediate the traction sheaves and the upper end of the boom. The outhaul line engages the sets of translatable sheaves. The sets of sheaves are powered for translation by a hydraulic cylinder mechanism. As the translatable sheaves are extended away from each other slack is taken out of the outhaul line, thus raising the grapple carriage. When the translatable sheaves are retracted toward each other, additional outhaul line is played out to lower the grapple carriage.

United States Patent 1191 Raven et al.

[ Apr. 1,1975

[ CONTINUOUS LINE YARDER WITH TRACTION AND EXTENSIBLE SHEAVE ASSEMBLIES [75] Inventors: James R. Raven, Bellevue; Frederic E. Langford, Redmond, both of Wash.

[73] Assignee: Formac International, Inc., Seattle,

Wash.

22 Filed: Oct. 26, 1972 211 App]. No.: 301,128

[52] U.S. Cl 212/89, 212/84, 254/189 [51] Int. Cl. B66c 21/00 [58] Field of Search 212/84, 96, 89, 83, 87, 212/90; 254/189, 185 R, 172

[56] References Cited UNITED STATES PATENTS 111,188 1/1871 Flad et a1 254/189X 943,032 12/1909 Miller 212/84 X 2,588,037 3/1952 Orton 254/189 X 3,323,780 6/1967 Erickson et a1. 254/185 R 3,378,232 4/1968 McIntyre et al 254/185 B 3,407,942 10/1968 McIntyre et al. 212/89 X 3,436,056 4/1969 Thompson 254/185 R 3,584,747 6/1971 Ekelund et al 212/89 X OTHER PUBLICATIONS Washington Iron Works-Washington Model 108,

Skylok, Yarder, Seattle, Washington, Nov. 1967, Side Two.

Primary Examiner-Richard A. Schacher Assistant Examiner-James L. Rowland Attorney, Agent, or Firm-Christensen, OConnor, Garrison & Havelka [57] ABSTRACT A continuous or single line yarding system employs a single winch drum. The yarding system employs a boom mounted on a platform at a first location and an outhaul block at a location remote from the first. A single main yarding line engages two sets of traction sheaves rotatably mounted on the boom. The traction sheaves are driven by a prime mover through a suitable transmission mechanism. Both ends of the single line extend to the upper end of the boom to form the inhaul line and outhaul line portions of the single main line. The outhaul line is strung from the boom to the outhaul block and inwardly toward the boom where it connects to a grapple carriage intermediate the boom and the outhaul block. The grapple carriage is suspended by a sheave from the outhaul line between the boom and the outhaul block. The inhaul line extends outwardly from the boom and is also connected to the grapple carriage. Two sets of sheaves which are translatable away from and toward each other are mounted on the boom intermediate the traction sheaves and the upper end of the boom. The outhaul line engages the sets of translatable sheaves. The sets of sheaves are powered for translation by a hydraulic cylinder mechanism. As the translatable sheaves are extended away from each other slack is taken out of the outhaul line, thus raising the grapple carriage. When the translatable sheaves are retracted toward each other, additional outhaul line is played out to lower the grapple carriage.

9 Claims, 7 Drawing Figures PAYEHIED APR 1 95 SHEET 1 CONTINUOUS LINE YARDER WITH TRACTION AND EXTENSIBLE SHEAVE ASSEMBLIES BACKGROUND OF THE INVENTION The present invention relates to yarding systems, and particularly to a yarding system in which the inhaul and outhaul lines are a continuous line which is driven by traction sheaves, in which tension and slack are provided in the outhaul line by a set of translatable sheaves, and in which a grapple is operated by a cable storage drum.

In prior art suspension yarding systems, a cable wound onto an outhaul drum mounted on a yarder platform is strung through an idler sheave at the end of a boom and outwardly from the boom to an outhaul block at a remote location. From the outhaul block the cable returns inwardly toward the boom and is connected to a carriage. The carriage can be suspended from a sheave on the outhaul line or from a separate carriage suspension line. An inhaul cable, wound onto an inhaul drum mounted on the platform is strung upwardly through an idler sheave on the end of a boom and outwardly to the carriage. In the first type of prior art yarding system a grapple operating line is wound onto a third drum, is strung upwardly through an idler sheave on the boom and outwardly to the carriage, and in turn is connected to actuate a grapple or other log grasping means on the carriage.

In a second type of prior art yarding system the outhaul line is arranged in the same manner as the first type described above. However, the inhaul line is wound onto an inhaul drum and strung through an idler sheave in the boom and outwardly toward the carriage. The inhaul line is strung around an idler sheave in the carriage, returned to another idler sheave in the boom, and wound onto a storage drum. A grapple operating line is connected to the inhaul line at a point inwardly from the carriage and is strung over a second idler sheave, after which it is connected to actuate the grapple. Differential payout of line between the inhaul drum and the storage drum actuates the grapple.

Both of these prior art systems require an outhaul drum, an inhaul drum and a grapple actuating or storage drum. Lowering or raising of the grapple carriage with respect to the ground is accomplished by differential payout of the inhaul and outhaul lines. Payout or inhaul of line must also be coordinated with respect to the grapple actuating line. Such prior art systems require the use of complex and expensive sets of clutches and brakes to differentially actuate the various drums.

simple to operate and relatively inexpensive to manufacture; a yarding system which can be utilized with a grapple or other suitable log handling means; a yarding system with a cable storage and grapple operating drum; a yarding system requiring only one primary operating shaft; a yarding system requiring a minimum of brake and clutch mechanisms for operation; a yarding system employing a boom on which all operational equipment is mounted except the prime mover means.

SUMMARY OF THE INVENTION The foregoing objects, and other objects which will become apparent upon reading the ensuing specification, are provided in a yarding system comprising (1) a carriage means having a log grasping means thereon, (2) a traction sheave means mounted for rotation on a first support, (3) an outhaul block means secured to a second support at a location remote from the first support, (4) a flexible rope means having an inhaul portion and an outhaul portion, (5) at least one pair of sheave means translatable toward and away from each other, and (6) a prime mover means for reversibly rotating said traction sheave means. The outhaul portion of the rope means is connected to the carriage means and is strung through the outhaul block means and extends back to the traction sheave means. The carriage means is suspended for movement from the outhaul portion of the rope means for movement between the traction sheave means and the outhaul block means. The inhaul portion of the rope means extends from the traction sheave means to the carriage means and is connected to the carriage means. The traction sheave means engages the rope meansin frictional driving relationship to move the carriage means between the outhaul block Alternatively, prior art systems have employed a relatively expensive mechanical differential which can be fluid or mechanically operated. Additionally, the operation of such yarding systems requires a great amount of skill and knowledge in the operator since the controls required are as complicated. as the system itself.

Objects of the present invention are to provide: a yarding system which eliminates a haulback drum; a yarding system which eliminates an inhaul drum; a yarding system which is relatively light and compact so that it can be moved from location to location; a yarding system in which the yarding distance can easily be varied; a yarding system which provides a novel means for raising and lowering the log handling carriage with respect to ground; a yardin g system which has a continuous inhaul and outhaul cable connected at its ends to the log handling carriage; a yarding system which is means and the traction sheave means. The carriage means can be traversed between the outhaul block means and the traction sheave means by rotating the traction sheave means in the appropriate direction. The rope means also engages the pair of sheave means at a location between the carriage means and the traction sheave means. Movement of the pair of sheave means toward each other increases the effective length of the rope means to lower the carriage means. Viceversa, movement of the pair of sheave means away from each other shortens the effective length of the rope means to raise the carriage means.

BRIEF DESCRIPTION OF THE DRAWINGS A better understanding of the present invention can be acquired by a reading of the ensuing specification in conjunction with the accompanying drawings wherein:

FIG. 1 is an isometric view of the log yarding system of the present invention;

FIG. 2 is an isometric pictorial representation of the cable driving mechanism of the yarding system of the present invention;

FIGS. 3, 4, and 5 are left side, front, and right side elevation views of the extensible sheave assembly employed in the cable driving mechanism of the present invention;

FIG. 6 is an enlarged pictorial representation of the cable storage drum and drive therefor; and

FIG. 7 is an isometric view of an alternate carriage block which can be utilized with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIG. 1 the yarding system of the present invention employs a boom which is pivotally mounted by pins 12 onto standards 14 of a suitable platform 16. An outhaul line 18 is connected to the distal or outhaul side of a grapple carriage 20 by a suitable connecting pin 22. The outhaul line 18 extends outwardly from the carriage 20 through an idler sheave in an outhaul block 24. The outhaul block 24 is anchored at a desired location remote from the yarding boom 10. The outhaul block 24 is usually anchored adjacent an area being logged and can be moved as desired laterally, outwardly, or inwardly from the boom 10. After traversing the outhaul block 24, the outhaul line 18 returns inwardly toward the carriage 20. The carriage 20 is suspended on the inwardly directed leg of the outhaul line 18 by means of a pulley block 26 fastened by a swivel to the carriage. The sheave within the pulley block 26 rests on top of the inward leg of the outhaul line 18. From the pulley block 26 the outhaul line 18 extends inwardly to an idler sheave 28 mounted on the end of the boom 10.

From the idler sheave 28 the outhaul line 18 engages idler sheave 30 and is wound about a first set 32 and second set 34 of sheaves, collectively referred to as the extensible sheave assembly 36. After engaging the extensible sheave assembly 36, the outhaul line 18 passes over idler sheave 38 and traverses a first set 40 and a second set 42 of traction sheaves. After transversing the sets 40 and 42 of traction sheaves, the continuous line again extends toward the top of the boom 10, engaging idler sheave 44. This portion of the continuous line will be referred to as the inhaul line 18a. After inhaul line 18a traverses the idler sheave 44, it extends outwardly to the carriage 20. In one form of the invention the inhaul line 18a loops around an idler sheave 46 in the carriage 20 and again returns to the boom 10. Although the line is also continuous at this point, the latter segment will be referred to as the grapple operating line 18b. Grapple operating line 18b traverses an idler sheave 48 mounted on the upper end of the boom 10, extends downwardly and is wrapped onto a payout or storage to a drum 50.

Outhaul line 18, inhaul line 18a and grapple operating line 18b are formed from a flexible rope, preferably a stranded wire cable. It will be noted that the cable has only two ends. One end is connected to the outhaul side of carriage 20. The other end is connected to the storage drum 50. When it is desired to increase the yarding distance, i.e. the distance between boom 10 and the location where outhaul block 24 is secured, line is payed out from storage drum 50 as the outhaul block 24 is moved further away from the boom 10. As this is done,

a portion of grapple operating line 18b becomes inhaul line 18a while a portion of the latter becomes outhaul line 18. When the yarding distance is to be decreased, line is wound onto the storage drum 50 as the outhaul block is moved closer to the boom 10.

A suitable donkey engine 52 is mounted on the platform 16 and drives a chain 54 through a suitable transmission 56. Chain 54 drives a sprocket 58 in turn drivingly connected to a shaft 60. Pinion 62, disengageably secured to shaft 60, drives a spur gear 64 which in turn drives a second shaft 66 journaled on the boom 10. The first set 40 of idler sheaves is secured to the shaft 66. As the chain 54 is driven in the direction of arrow 68, the line 18 engaging the traction sheaves 40 and 42 will be driven in the direction of arrow 70. In so doing the inhaul line 180 will be drawn in the direction of arrow 72, while outhaul line 18 will be driven in the direction of arrow 74. Thus the carriage 20 will be drawn inwardly toward the boom 10. As shown, a log can be carried from the remote location adjacent outhaul block 24 toward a logging platform adjacent the boom 10 in this mode of operation.

When chain 54 is driven in the direction opposite to arrow 68 by reversing the transmission 56, outhaul line 18 is drawn toward the boom while inhaul line 18a is driven outwardly, thus returning the carriage 20 to the remote location adjacent block 24.

In normal yarding operations the inhaul and outhaul lines are maintained relatively taut when moving the carriage both away from and toward the boom 10. When the carriage 20 reaches the remote location, it is lowered so that a log 76 can be secured by the grapple 78. Thereafter, the carriage 20 and log 76 are raised above the ground so that the log is not dragging on the ground as it is returned toward the boom. As shown in ghost outline, the carriage 20 has been raised to the position 80 by maintaining tension in the inhaul and outhaul lines as the carriage 20 is moved toward the outhaul block 24.

The yarding system of the present invention accomplishes raising and lowering of the carriage 20 by increasing or decreasing the amount of outhaul line between the boom 10 and block 24. Varying the amount of line extending from the boom is accomplished through use of the extensible sheave assembly 36 mounted on the boom 10. To decrease the amount of outhaul line extending from the boom 10, the extensible sheave assembly is actuated to the position 82 shown in ghost outline. The sheave assembly is extended by means of a double-acting hydraulic cylinder mechanism 84 which interconnects the first set of sheaves 32 with the second set of sheaves 34. The first set of sheaves 32 is secured to the boom 10 by means of block 86 connected to bracket 88. One end of the hydraulic cylinder 84 is also attached to bracket 88. Block 90, rotatably supporting the second set of sheaves 34, is connected to the other end of the cylinder 84. Thus the second set of sheaves 34 is powered for reciprocal translation away from and toward the first set of sheaves 32.

As the second set of sheaves 34 is moved to the position shown in ghost outline as 82, an amount of outhaul line 18 is taken up by the assembly 36 which is proportional to the number of cable strands traversing the sets of sheaves 32 and 34. When the second set of sheaves 34 is translated toward the first set 32 as shown in primary outline, outhaul cable 18 is payed out, thus lowering the carriage 20 to the position shown in primary outline. It is of course to be understood that the extensible sheave assembly can be utilized in conjunction with either the inhaul line 18a or the outhaul line 18, although the latter is preferred.

Referring now to the pictorial isometric of the cable driving system mechanisms in FIG. 2, the output shaft of the donkey engine 52 is fixed to a gear 96 driving a chain 98 which in turn drives the input shaft of a hydraulic pump 100. The pump 100 draws hydraulic fluid from a sump 102 through conduit 104. The output from pump 100 is directed through output conduit 106 to a three-position four-way valve 108. A return line is also provided between the valve 108 and the sump 102. When the valve 108 is in the first position 108a, hydraulic fluid is returned to the sump via return conduit 110. In the second position, 108b, hydraulic fluid is directed through the valve into a conduit 112 which is connected by a Y-coupling to each end of the double-acting hydraulic cylinder 84 on the extensible sheave assembly 36. When the valve 108 is in the second position 108b, the hydraulic fluid directed to cylinder 84 acts to expand the extensible sheave assembly 36 to decrease the amount of available outhaul line 18. In the third position 1086 hydraulic fluid from the pump 100 is returned to the sump by conduit 110. In addition the double actinghydraulic cylinder is drained, retracting the extensible sheave assembly 36. The fluid from the hydraulic cylinder 84 is also returned to the sump 110. In the first position 108a no hydraulic fluid is allowed to flow to or from the cylinders, thus locking them in a given desired position.

The output shaft of the donkey engine 52 is also drivingly connected to a transmission 56. Transmission 56 preferably is of a variable speed forward and reverse type. Suitable transmissions of this type are available in the art. The output shaft 114 of the transmission 56 drives a clutch 116 and a brake 118. The output of clutch 116 drives shaft 115, the latter of which drives a drive sprocket 120 meshing with chain 54 in turn driving driven sprocket 58. Sprocket 58 is fixed to shaft 60 on which pinion 62 is journaled. Pinion 62 is driven through clutch 122 which incorporates a brake 123. One side of clutch 122 is fixed to shaft 60 while the output side is fixed to pinion 62. When clutch 122 is disengaged pinion 62 rotates freely on the shaft 60.

Pinion 62 drives spur gear 64 which is fixed to driven shaft 66. As explained above the set 40 of traction sheaves is also connected to shaft 66. Cable storage drum 50 is rotatably journaled on the driven shaft 66. Referring to FIGS. 2 and 6, gear 124 is affixed to drum 50 and is driven by pinion 126. Pinion 126 is journaled for rotation of the shaft 60 and is engageable to shaft 60 through the clutch 128 and brake 130. To drive the storage drum 50 in conjunction with the idler sheave 40 the clutch 128 is engaged. To allow the storage drum 50 to rotate freely on the shaft 66 while the idler sheave 40 is being driven, clutch 128 is disengaged. Drum 50 can be slowed or stopped by engaging in brake 130.

As shown in FIG. 6, a second clutch 131 has one side connected to shaft 66 with the output side connected to driven gear 124. Thus drum 50 can be directly driven by the shaft 66 in conjunction with traction sheaves 40. By properly sizing the diameter of drum 50 relative to the diameter of sheaves 40 and by choosing the gear ratio between pinion 126 and gear 124 relative to the ratio of main pinion 62 and gear 64, the drum 50 can be operated at different peripheral speeds during outhaul and inhaul of line 18b. By driving drum 50 in this manner, slipping of clutches 128 and 131 necessary to accommodate the varying wrap diameter of line 18b on the storage drum and to maintain line 18b in a slack condition during inhaul and outhaul can be minimized.

Referring back to FIG. 1 thegrapple 78 is operated by relative movement of the grapple operating line 18b and the inhaul line 18a with respect to the carriage 20. A secondary grapple operating line 134 is connected to a stop-block 136 securely affixed to the grapple operating line 18b. Secondary line 134 traverses an idler sheave 138 mounted in the carriage 20 and is connected to the pivot pin 140 between the arms of the grapple 78. When the grapple operating line 18b is payed out in the direction of arrow 142 relative to movement of the carriage 20, slack occurs in secondary line 134 causing the arms of the grapple 178 to relax and grasp the log 76 within its jaws'. When the grapple operating line 18b is drawn in in a direction opposite to arrow 142, secondary line 134 is drawn upwardly, spreading the jaws of the grapple 78 to release the log 76.

To operate grapple 78 the set 40 of traction sheaves and the payout drum 50 are differentially driven in either direction by means of an operative combination of engaging and disengaging clutches 122 and 128 and applying brakes 123 and (FIG. 2).

Referring again to FIG. 2 a straw drum 144 is also rotatively journaled on the main shaft 60. Straw drum 144 can be drivingly interconnected with shaft 60 through the clutch 146. A brake 148 is also connected to the straw drum 144. As shown in FIG. 1 the straw cable 150 traverses a bulls-eye fairlead 152 mounted on the boom 10. Straw line 150 can be used primarily as a winch to draw equipment and/or other loads toward the boom 10 as desired.

Referring now to FIGS. 3, 4 and 5, left side elevation, plan view and right side elevation views of the extensible sheave assembly 36 are shown. Referring jointly to these FIGURES extensible sheave assembly 36 is attached at its lower end to boom 10 by means of bracket 88. The bracket 88 is fastened to a cross member 154 of,the boom 10 by suitable fastening means 156. The bracket 88 is connected to the lower block 86 in which the first set of sheaves 32 is journaled on a shaft 158. Bracket 88 also supports lower hydraulic cylinder 163. The outhaul line 18 extends downwardly from the top end of the boom (not shown) and engages a first idler sheave 30. Idler sheave 30 is attached by a flange 162 to the top cylinder section 164 of the double acting hydraulic cylinder mechanism 84. The outhaul line 18 descends below idler sheave 30, engages one of the sheaves of the first set 32, and traverses upwardly toward the second set of sheaves 34. The second set of sheaves 34 are journaled by an appropriate shaft 166 in a block 90 attached to top cylinder 164. Line 18 traverses the sets 32 and 34 of sheaves as many times as there are individual sheaves, in this embodiment three on each set. Line 18 ultimately spans from a sheave in the second set 34 downwardly onto idler sheave 38 and onto the set 42 traction sheaves (FIG. 1). The lower idler sheave 38 is connected to an arm 170 in turn connected to the block 86.

As shown in FIG. 4, the extensible sheave assembly 36 can be extended between a retracted position as shown in primary outline out to and beyond an extended position 174 as shown in ghost outline. Depending on the number of individual sheaves in each of the sets 32 and 34 an amount of outhaul line 18 equal to twice the extension of the assembly times the number of sheaves per set can be payed out or retracted as desired. The primary purpose of the extensible sheave assembly 36 is to provide a quick, efficient and inexpensive way to raise and lower the grapple carriage for yarding. Extensible sheave assembly 36 can be used also to slacken or tighten the lines 18 for a minor adjustment caused by differential rotation of the storage drum 50 (FIG. 2). It is not preferred that it be used for the latter operation since it is desirable to employ the full extension and retraction of the assembly 36 for purposes of raising and lowering the carriage.

An alternate embodiment of the carriage assembly is shown in FIG. 7. In this embodiment the outhaul line 18 is connected to a pin 180 on one side of the carriage 182 and is strung through the pulley 184. The inhaul line 18a traverses an idler sheave 186 in the carriage 182 and returns to the boom as the storage line 18b. For this usage a removable clamp or stop block 136 can be employed to rest against the inward side of the carriage. Thus line 18b can always be operated in a slack condition in this embodiment. In this embodiment the line 188, a choker cable or other suitable means for hauling a load, is connected by pin 190 to the carriage 182 for hauling from a remote location back to the boom.

The present invention has been described in relation to preferred embodiments of the invention. Various changes, alterations and substitution of equivalents can be made by one of ordinary skill in the yarding art without departing from the original concept of the invention. It is therefore intended that the invention be limited only the difinition contained in the appended claims.

What is claimed is:

l. A yarding system comprising:

a carriage means having log grasping means thereon,

traction sheave means mounted for rotation on a first support, an outhaul block means secured to a second support at a location remote from said first support,

flexible rope means having an inhaul portion and an outhaul portion, said outhaul portion being connected to said carriage means and being strung through said outhaul block means and back to said traction sheave means, said carriage means being suspended for movement from said outhaul portion of said rope means at a location between said traction sheave means and said outhaul block means, said traction sheavev means engaging said rope means in frictional driving relationship, said inhaul portion extending from said traction sheave means to said carriage means and being connected to said carriage means,

at least one pair of sheave means translatable toward and away from each other, said rope means engaging said pair of sheave means at a location between said carriage means and said traction sheave means, whereupon movement of said pair of sheave means away from each other shortens the effective length of said rope means to raise'said carriage means and movement of said pair of sheave means toward each other increases the effective length of said rope means to lower said carriage means, and

prime mover means for reversibly powering said traction sheave means.

2. The yarding system of claim 1 further comprising:

an idler sheave mounted for rotation on said carriage means,

payout drum means rotatably mounted on said first support, said rope means further comprising a payout portion, said payout portion being an extension of said inhaul portion, said payout portion engaging said idler sheave and extending through said carriage means to said payout drum means, transmission means driven by said prime mover means for rotating said payout drum means with said traction sheave means and for rotating and stopping said payout drum means independently of said traction sheave means, and

adjustable stop means removably fixed to said payout portion of said rope means and capable of abutting engagement with said carriage means for limiting the amount of-said payout portion of said rope means which can be payed out from said payout drum means through said carriage means.

3. The yarding system of claim 2 further comprising:

grapple means operably suspended from said carriage means, and

an actuating line operatively connected to said grapple means and to said rope means to close and open said grapple means responsive to movement of said payout portion of said rope means relative to said carriage means.

4. The yarding system of claim 2 wherein said first support comprises a boom, said traction sheave means and said payout drum means being mounted on a first shaft rotatably mounted on said boom, said payout 25 drum means being rotatably mounted on said shaft.

5. The yarding system of claim 4, wherein said traction sheave means comprises:

a first set of sheaves mounted on said first shaft and a second set of sheaves mounted on a second shaft 3 parallel to and spaced from said first shaft, said second shaft rotatably mounted on said boom, said rope means alternately engaging a sheave on said first set and a sheave on said second set.

6. The yarding system of claim 2 further comprising:

means for driving said payout drum means in a first direction at a first predetermined speed and in a second direction at a second predetermined speed.

7. The yarding system of claim 1 wherein one of said pair of sheave means is connected to said first support, the other of said pair of sheave means being movable with respect to said first support.

8. The yarding system of claim 1 wherein said pair of sheave means comprises:

a first set of sheaves and a second set of sheaves, said rope means alternately engaging a sheave in said first set and a sheave in said second set, said first set of sheaves being mounted on said first support, and

means mounting said second set of sheaves for reciprocal movement toward and away from said first set of sheaves.

9. The yarding system of claim 8 wherein said means for mounting said second set of sheaves for reciprocal movement comprises:

hydraulic cylinder means actuated by supplying hydraulic fluid thereto, said hydraulic cylinder means being mounted between said first and second set of sheaves, and

means for supplying hydraulic fluid to said cylinder means, said means for supplying hydraulic fluid being powered by said prime mover means. 

1. A yarding system comprising: a carriage means having log grasping means thereon, traction sheave means mounted for rotation on a first support, an outhaul block means secured to a second support at a location remote from said first support, flexible rope means having an inhaul portion and an outhaul portion, said outhaul portion being connected to said carriage means and being strung through said outhaul block means and back to said traction sheave means, said carriage means being suspended for movement from said outhaul portion of said rope means at a location between said traction sheave means and said outhaul block means, said traction sheave means engaging said rope means in frictional driving relationship, said inhaul portion extending from said traction sheave means to said carriage means and being connected to said carriage means, at least one pair of sheave means translatable toward and away from each other, said rope means engaging said pair of sheave means at a location between said carriage means and said traction sheave means, whereupon movement of said pair of sheave means away from each other shortens the effective length of said rope means to raise said carriage means and movement of said pair of sheave means toward each other increases the effective length of said rope means to lower said carriage means, and prime mover means for reversibly powering said traction sheave means.
 2. The yarding system of claim 1 further comprising: an idler sheave mounted for rotation on said carriage means, payout drum means rotatably mounted on said first support, said rope means further comprising a payout portion, said payout portion being an extension of said inhaul portion, said payout portion engaging said idler sheave and extending through said carriage means to said payout drum means, transmission means driven by said prime mover means for rotating said payout drum means with said traction sheave means and for rotating and stopping said payout drum means independently of said traction sheave means, and adjustable stop means removably fixed to said payout portion of said rope means and capable of abutting engagement with said carriage means for limiting the amount of said payout portion of said rope means which can be payed out from said payout drum means through said carriage means.
 3. The yarding system of claim 2 further comprising: grapple means operably suspended from said carriage means, and an actuating line operatively connected to said grapple means and to said rope means to close and open said grapple means responsive to movement of said payout portion of said rope means relative to said carriage means.
 4. The yarding system of claim 2 wherein said first support comprises a boom, said traction sheave means and said payout drum means being mounted on a first shaft rotatably mounted on said boom, said payout drum means being rotatably mounted on said shaft.
 5. The yarding system of claim 4, wherein said traction sheave means comprises: a first set of sheaves mounted on said first shaft and a second set of sheaves mounted on a second shaft parallel to and spaced from said first shaft, said second shaft rotatably mounted on said boom, said rope means alternately engaging a sheave on said first set and a sheave on said second set.
 6. The yarding system of claim 2 further comprising: means for driving said payout drum means in a first direction at a first predetermiNed speed and in a second direction at a second predetermined speed.
 7. The yarding system of claim 1 wherein one of said pair of sheave means is connected to said first support, the other of said pair of sheave means being movable with respect to said first support.
 8. The yarding system of claim 1 wherein said pair of sheave means comprises: a first set of sheaves and a second set of sheaves, said rope means alternately engaging a sheave in said first set and a sheave in said second set, said first set of sheaves being mounted on said first support, and means mounting said second set of sheaves for reciprocal movement toward and away from said first set of sheaves.
 9. The yarding system of claim 8 wherein said means for mounting said second set of sheaves for reciprocal movement comprises: hydraulic cylinder means actuated by supplying hydraulic fluid thereto, said hydraulic cylinder means being mounted between said first and second set of sheaves, and means for supplying hydraulic fluid to said cylinder means, said means for supplying hydraulic fluid being powered by said prime mover means. 